Activation of transmit/receive arrays for decoupling during transmission

Abstract

A system for electromagnetic excitation of an object under examination during magnetic resonance tomography includes a radio frequency (RF) device for generating a radio-frequency signal and a plurality of antennas for emitting the radio-frequency signal. A signal connection exists between the output of the RF device and the plurality of antennas. A source impedance of the signal connection to the output of the RF device at a connection point of the plurality of antennas is significantly higher than the impedance of the plurality of antennas at the connection points, so that the plurality of antennas are fed in a current source feed mode if a radio-frequency signal is present.

The invention claimed is: 
     
       1. A system for electromagnetic excitation of an object under examination during magnetic resonance tomography, the system comprising:
 a radio frequency (RF) device configured to generate a radio-frequency signal; 
 a plurality of antennas configured to emit the radio-frequency signal; and 
 a signal connection between an output of the RF device and the plurality of antennas, 
 wherein a source impedance of the signal connection with the output of the RF device at connection points of the plurality of antennas is higher than an impedance of the plurality of antennas at the connection points, so that the plurality of antennas are fed in a current source feed mode when the radio-frequency signal is present. 
 
     
     
       2. The system as claimed in  claim 1 , wherein the source impedance of the signal connection with the output of the RF device at the connection points of the plurality of antennas is higher by at least a factor of 2 than the impedance of the plurality of antennas at the connection points. 
     
     
       3. The system as claimed in  claim 2 , wherein the RF device further comprises an input operable to process a receive signal,
 wherein the system further comprises a switch and a signal connection between an input of the RF device and the plurality of antennas, and 
 wherein the switch is configured to optionally connect the plurality of antennas to the output of the RF device or to disconnect the plurality of antennas from the output of the RF device. 
 
     
     
       4. The system as claimed in  claim 1 , wherein the RF device further comprises an input operable to process a receive signal,
 wherein the system further comprises a switch and a signal connection between an input of the RF device and the plurality of antennas, and 
 wherein the switch is configured to optionally connect the plurality of antennas to the output of the RF device or to disconnect the plurality of antennas from the output of the RF device. 
 
     
     
       5. The system as claimed in  claim 4 , wherein a connection impedance of the signal connection to the input of the RF device at the connection points of the plurality of antennas is higher than the antenna impedance at the connection points. 
     
     
       6. The system as claimed in  claim 5 , wherein the connection impedance of the signal connection to the input of the RF device at the connection points of the plurality of antennas is higher by at least a factor of 2 than the impedance of the plurality of antennas at the connection points. 
     
     
       7. The system as claimed in  claim 1 , further comprising an RF activation matrix configured to distribute the radio-frequency signal from the output of the RF device to the connection points of the plurality of antennas with a predetermined impedance and a respective predefined phase offset for each antenna of the plurality of antennas. 
     
     
       8. The system as claimed in  claim 7 , wherein an arrangement of the plurality of antennas and the predefined phase offset are configured such that the plurality of antennas generate a circular-polarized electromagnetic alternating field. 
     
     
       9. The system as claimed in  claim 1 , wherein the plurality of antennas are antenna coils. 
     
     
       10. The system as claimed in  claim 9 , wherein surfaces of the plurality of antenna coils overlap such that an interaction of two neighboring surfaces is minimized. 
     
     
       11. A magnetic resonance tomograph comprising:
 a system for electromagnetic excitation of an object under examination during magnetic resonance tomography, the system comprising:
 a radio frequency (RF) device operable to excite a radio-frequency signal; 
 a plurality of antennas operable to emit the radio-frequency signal; and 
 a signal connection between an output of the RF device and the plurality of antennas, 
 
 wherein a source impedance of the signal connection with the output of the RF device at connection points of the plurality of antennas is higher than an impedance of the plurality of antennas at the connection points, so that the plurality of antennas are fed in a current source feed mode when the radio-frequency signal is present. 
 
     
     
       12. The magnetic resonance tomograph as claimed in  claim 11 , wherein the source impedance of the signal connection with the output of the RF device at the connection points of the plurality of antennas is higher by at least a factor of 2 than the impedance of the plurality of antennas at the connection points. 
     
     
       13. The magnetic resonance tomograph as claimed in  claim 12 , wherein the RF device further comprises an input operable to process a receive signal,
 wherein the system further comprises a switch and a signal connection between an input of the RF device and the plurality of antennas, and 
 wherein the switch is configured to optionally connect the plurality of antennas to the output of the RF device or to disconnect the plurality of antennas from the output of the RF device. 
 
     
     
       14. The magnetic resonance tomograph as claimed in  claim 11 , wherein the RF device further comprises an input operable to process a receive signal,
 wherein the system further comprises a switch and a signal connection between an input of the RF device and the plurality of antennas, and 
 wherein the switch is configured to optionally connect the plurality of antennas to the output of the RF device or to disconnect the plurality of antennas from the output of the RF device. 
 
     
     
       15. The magnetic resonance tomograph as claimed in  claim 14 , wherein a connection impedance of the signal connection to the input of the RF device at the connection points of the plurality of antennas is higher than the antenna impedance at the connection points. 
     
     
       16. The magnetic resonance tomograph as claimed in  claim 15 , wherein the connection impedance of the signal connection to the input of the RF device at the connection points of the plurality of antennas is higher by at least a factor of 2 than the impedance of the plurality of antennas at the connection points. 
     
     
       17. The magnetic resonance tomograph as claimed in  claim 11 , further comprising an RF activation matrix configured to distribute the radio-frequency signal from the output of the RF device to the connection points of the plurality of antennas with a predetermined impedance and a respective predefined phase offset for each antenna of the plurality of antennas. 
     
     
       18. The magnetic resonance tomograph as claimed in  claim 17 , wherein an arrangement of the plurality of antennas and the predefined phase offset are configured such that the plurality of antennas generate a circular-polarized electromagnetic alternating field. 
     
     
       19. The magnetic resonance tomograph as claimed in  claim 11 , wherein the plurality of antennas are antenna coils. 
     
     
       20. The magnetic resonance tomograph as claimed in  claim 19 , wherein surfaces of the plurality of antenna coils overlap such that an interaction of two neighboring surfaces is minimized.